Electronic equipment according to the above is often portable. A common example of a portable electronic apparatus is a mobile terminal having a wireless telecommunication interface to a mobile telecommunications network compliant with for instance GSM, UMTS, D-AMPS, CDMA2000, FOMA or TD-SCDMA. A typical mobile terminal 200 is shown in FIG. 2a in the form of a mobile phone. In a well known manner, this prior art mobile terminal 200 comprises a speaker or earphone 202, a microphone 205, a display 203 and a set of keys 204 which includes a 12-button keypad 204a of common ITU-T type (alpha-numerical keypad representing characters “0”-“9”, “*” and “#”), and soft keys 204b, 204c. In addition, a joystick 211, or other type of navigational input device (e.g. scroll keys, touchpad, four/five-way navigation key, or rotator), is also provided. Other well known but not illustrated external components include volume control keys, power-on button, battery, charger interface and accessory interface.
Market demands have forced mobile terminals to become smaller and smaller. The 12-button ITU-T keypad is a limiting factor in this respect which restricts the design of mobile terminals, since it must have certain physical minimum dimensions in order to remain operable by the fingers of a human user.
On the other hand, the ITU-T keypad plays several important roles in modern mobile terminals and do not function only as a dialing keypad for manual entry of telephone numbers to call, but also as an alpha-numeric keyboard for text entry, as a game control for video games, etc. As regards text entry, each key in the ITU-T keypad often relates to several characters. A single key may, for instance, relate to the characters “a”, “b” and “c”. Pressing the key once produces the character “a”, pressing the key twice within a short period of time produces the character “b”, and pressing the key three times within a short period of time produces the character “c”. Pressing the button twice slightly more slowly produces two “a”:s. It is rather slow to use an ITU-T keypad in this a manner for character input; therefore, various methods for facilitating text entry with an ITU-T keypad have been developed. One well known example is T9 character prediction functionality.
The users of input mechanisms based on ITU-T keypad with character prediction functionality will have indirect access to the target character in the sense that they can press a key that represents 3-6 characters (e.g., “abc” on key “2”). This indirectness implies that a user will easily locate the target character. However, the prediction functionality has the negative effect that the user needs to validate the input on display—e.g., whether hitting the “2” key is interpreted as “a”, “b” or “c”. This is a negative aspect that typically requires time consuming user validation.
Attempts have been made to replace the relatively large ITU-T keypad with an alternative but much smaller input device. For instance, some prior art mobile phones use a mechanical rotator with character prediction functionality for character input. The rotator is typically used for navigating among a presented alphabetical character sequence with an appended set of prediction characters available for selection. While these devices have proven easy to learn for the users, experience nevertheless shows that even expert users will suffer from slow character input rates. The reasons for this are believed to include the following.
1) If the prediction characters do not match with the user's target character, the user has to potentially scroll many turns on the mechanical rotator to locate and find the target character in the alphabetical sequence; determining whether the target character is among the predicted characters and the many turns on the rotator are time consuming and slow down overall performance.
2) Each time the target character is found and highlighted—whether through the prediction characters or the alphabetical sequence—the user needs to lift his finger from the rotator and move it to a separate select key to select the highlighted character, and to continue the character input the finger needs to be moved back to the rotator. Both these finger movements are time consuming, and even for an expert user this time penalty cannot be compensated.